In general, a core technology of a solar cell using a bulk-structured polycrystalline silicon thin film is to form a polycrystalline silicon thin film on a glass substrate, i.e., a low-cost substrate.
Since it may be impossible to form a polycrystalline silicon thin film on an amorphous glass substrate in terms of processing, an amorphous silicon thin film is formed. Then, a polycrystalline silicon thin film is formed by performing a crystallization process as a post process.
As a typical crystallization method, there is a method of using heat. However, since amorphous silicon is crystallized at a higher temperature than a melting point of a glass substrate, the above method has been regarded as an impossible method.
Recently, research into various crystallization methods has been conducted mainly in industrialized countries, and metal induced crystallization (MIC), laser crystallization (LC), and joule induced crystallization (JIC) have typically been known.
With respect to MIC, as a method of crystallization while stacking metal (aluminum (Al), nickel (Ni), and gold (Au)) and amorphous silicon and applying heat below the melting point of a glass substrate, it has a limitation in application to a high-quality solar cell due to metal residues.
With respect to JIC, as a method of crystallization by forming an electrode on an amorphous silicon thin film and temporarily applying an induced current, since the adhesiveness of the thin film may be weak and a phenomenon of peeling off the thin film may be severe, reproducibility may be reduced.
With respect to LC, it is a reliable method of providing a high-quality product by crystallization. However, because a substrate is scanned with a laser beam, a shot mark phenomenon, which is caused by the non-uniformity of energy generated during the LC, may occur, it may take a long time, and cost may be basically high.